DKIM for Exchange Server

I stumbled upon this commercial application implementing DKIM for IIS SMTP and Exchange 2000/2003/2007 from AdminSystem Software. I have not used it, but I will test their free trial. I do sometimes hear people ask how and if it is possible to deploy DKIM on Exchange.

The price is $299 US per server, but applies to all SMTP domains for that server. Product documentation is also available online.